The invention relates to a fuel injection apparatus as defined hereinafter. In a fuel injection device of this type, known from German Utility Model No. DE-GM 83 21 888, the flow control device is embodied as a slide valve, and the pump piston serves as the movable valve member. With an oblique control edge on its jacket face, this pump piston causes the outlet of the relief conduit on the circumferential wall of the pump cylinder to communicate with the pump work chamber beyond a pump supply stroke that is defined by the rotational position of the pump piston. In this way, the rotational position of the pump piston determined the quantity of fuel attaining injection at high pressure per pumping stroke. Fuel injection devices of this type are embodied in particular, as also shown in the above patent document, as units comprising a fuel injection pump and fuel injection valve, with a very short pressure line, of stable shape, located between the pump work chamber and the injection valve opening; they are used for attaining accurate injection even with internal combustion engines which operate at very high speeds and in which there is direct injection into the combustion chambers. In such engines, in order to attain good fuel preparation within the abbreviated time that is available for ignition delay and combustion of the injected fuel in this case, it is necessary to assure accurate and very fast control of the injection valve closing member and also, for the sake of better atomization of the injected fuel, to operate at an elevated injection pressure.
In the known fuel injection apparatus, furthermore, a pressure valve having a closing member is provided in the injection line leading on from the pump work chamber to the injection port of the injection valve. The closing member is cylindrical, with a pressure shoulder adjacent to the valve seat face, and it is acted upon from behind by a valve spring. The rear side, toward the valve spring, of the pressure valve closing member in this case communicates with the fuel injection line leading from the pressure valve closing member valve seat to the injection port; this is also the case, for example, in a unit fuel injector known from U.S. Pat. No. 4,158,442. The pressure valve closing members disclosed in these patent documents cannot function as equal-pressure valves, because in any case after the effective pump supply stroke has ended, with the pressure valve closing member located in its closing position, the pressure surface of the pressure valve closing member acting in the closing direction is larger than the one acting in the opening direction. Additionally, the pressure valve closing member is also urged in the closing direction by the valve spring. Injection devices of thie type have the disadvantage that at the end of the effective supply storke, immediately after the closure of the pressure valve closing member, pressure waves may flow back and forth in the fuel injection line between the pressure valve closing member and the injection port of the fuel injection valve, which can result in the brief opening of a fuel injection valve closing member that opens under pressure. As a result, after the intended end of the fuel injection process, some fuel is delivered to the combustion chamber belatedly and thus no longer burns, causing carbonization of the injection ports of the fuel injection valve. This process also contributes to an incorrect fuel injection quantity.
At the injection onset, in the known fuel injection devices discussed above the pressure valve closing member is deflected only far enough that the fuel positively displaced by the pump piston can flow past the valve closing member in such quantities as emerged at the injection port of the fuel injection valve after the valve closing member rose from its seat.